Port item up down movers from IntelliJ

[matklad]

Intellij Rust has this bunch of code:

https://github.com/intellij-rust/intellij-rust/tree/25f37175094192ba88f345f03b2a4b5b941dd395/src/main/kotlin/org/rust/ide/actions/mover

this is for moving items, statements and mactch arms up and down. rust-analyzer should have this as well, although I don't think that this is exposed in the procol. Rough steps:

• design appropriate LSP protocl extensions (see lsp-extensions.md)
• implement in the ide crate. This only needs access to syntax, so should be rather trivial.
• add a bunch of tests

[kjeremy]

Alternatively could we do this with a command?

[matklad]

Yeah, that would need to be a command in VS Code, and a request-response in LSP. The user can then bind the command to ctrl+shift+up/down or whatever

[kjeremy]

I think the LSP side could be a command as well to avoid another custom request/response.

[matklad]

Ah, sorry, I've misunderstood. Your idea is that the client will send workspace/executeCommand, and the server would use workspace/applyEdit?

If that's right, I'd rather do a custom extension still, for two reasons:

• I am not a fan of server-side initiated applyEdit, as that loses causality
• THis will still require custom per editor code to surface the command in the UI.

[kjeremy]

Yes that was the idea. You would still need custom code to surface the command of course but the benefit to other clients is that they wouldn't have to write as much.